X-ray tube



March 24, 1925. 1,530,555

G. R. GREENSLADE 'x-RAY TUBE Filed May 1922 Patented Mar. 24, 1925.

UNITED STATES PATENT OFFICE.

GBOVER R. GREENSLADE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO J. ROGERS FLANNEBY, OF PITTSBURGH, PENNSYLVANIA.

, x-RAY TUBE.

Application filed May 24, 1922. Serial No. 503,294.

To all whom it may concern Be it known that I, GROVER R. GREEN SLADE, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have The invention relates to Xray tubes. Its

objects are to provide an X-ray tube which 'f acts to rectify the current even at very high voltages, thus dispensing with the use of outside rectifiers and'enabling the associ-j ated and control apparatus tobe simplified;

which is more durable than similar tubes as heretofore constructed, from the fact that it requires no heatedv filament associated with the cathode; and which can operate on a lower voltage than prior forms of X-ray tubes, and hence reduces the liability of burnin" the patient. i

In the accompanying .drawing Fig. 1 shows the improved X-ray tube in section, and Fig. 2 is an enlarged detail view of the electrodes.

The tube comprises a vessel 1, which may be of the usual form and is exhausted toany degree desired. In this tubeis the cathode or mirror 2 and the anode or target 3, which are connected to the outside circuit by simple leading-in wires sealed in the ends ofthe I tube in the usual way.

Rectifying X-ra'y tubes as heretofore constructed have had associated with the cathode a filament arranged to be heated to incandescence by additional circuit connections through one end of the tube and supplied with a heatin current either from a storage battery or from taps taken off the secondary of the voltage increasing transformer, said hot filament radiating electrons or other emissions which form a uni- I lateral conducting path to the anode. The

life of such filaments, however, is limited, and to heat'the same requires additional leading-in wires and circuit arrangements and devices. Furthermore, such tubes do not operate at very high voltages. Therev is acertain limit of permissible voltage;

above whichsuch tubes begin to flutter and hence cease to 'rectif Inthe improved -ray tube, the hot filament and the circuit connections to it are entirely dispensed-with, and a. unilaterally conducting ath, or at least one having greater con uctivity in one directionthan in the other, between the cathode and anode is provided by the emissions or radiations rom a radio-active substance or substances associated with the cathode or with both the cathode and anode. The radio-active substance may be radium, uranium, actinium, thorium, or other radio-active substance or substances, or compounds thereof. Such substance or substances may be associated with the electrodes in any suitable way, such as coating or painting the compound on the face of a metallic electrode, or fusing the radio-active material thereto, or alloying it therewith.

The above radio-active materials and their disintegration products emit three forms of rays, to-wit, gamma rays, which are oscillatory disturbances of the character of light rays but of very high frequency, alpha rays, which are small particles, or, strictly speaking, atoms of helium gas and carry positive electrical charges, and beta rays which are electrons and constitute negative electrical charges. Hence the radio-active materials or products are preferably associated with the cathode in a manner to control the emission of the alpha rays, in order that the particles composingsuch rays will not fillthe space in the tube which would destroy the unilateral conductive characteristic of the tube. A convenient way of doing this is illustrated in the drawing, in which the body of thecathode 2 may be of any suitable metal, although for the purpose of I the; proper density and proper thickness alpha rays can be entirely out ofl, without in -cataat 6, Fig. 2, which emitsl onl largely alpha (rays, which carry positive 'trical charges. Thus b by the beta rays. It has beenfound that a foil of aluminum of 7/1Q0 millimeters in thickness gives good practical results, that is, it intercepts all or substantially all the alpha rays and only a small amount of the beta rays. The screen, however, can be of material other than aluminum, but if made of a denser metal it must be made thinner than above specified.

A cathode of the character described is substantially a cold cathode. Since there is no hot filament, the tube. is more durable than present forms of X-ray rectifying tubes. It requires no circuit connections to it other than the simple'circuit connections for the main current, and hence the outside apparatus may be of the simplest character'- electrical charges. "The same effect can be produced by applying to the anode a radioactive subst'ance which emits rays of several kinds, and so. screening or otherwise controlling this substance as to emit only or largely rays which carry positive elechaving rays emitted by the two :electro es which constitute or carry opposite electrical charges, the unilateral conductive characteristics of the intervening space is enhanced.

The invention is not dependentupon any particular degree of exhaustion of the tube. The tube may be exhausted either wholly or partially, but need be exhausted only tosuch degree that ionization is reduced to a point electrodes is rendered of equal conductivity.

therefore can be used without outside rec-- tifiers at voltages much higher than the present form of hot filament X-ray tubes. Furthermore the'conducting path produced by the radio-active emissions permits the high tension electric current to pass with greater ease so that the tube can be used with a current of lower voltage than with prior forms, of tubes, thus reducing the. danger of burning the patient and making the apparatus as a whole easier to handle and safer to use, and even safe for use by relatively unskilled operators.

The effect of the radio-active substance on the cathode may be enhanced by applying to the anode another radio-active substance which emits rays which carry opposite electrical charges from those permitted to be radiated by the cathode. For'instance, if the cathode has associated with it a radioactive substance which emits only beta rays, or is screened or controlled to permit of the passage only, or substantially only, of beta rays, which constitute negative electrical charges, the anode should have. applied thereto or associated therewith a radiothe radio-active substance in active substance, for example polonium, as

below that at which the space betweenthe in both directions. The invention is also applicable to tubes containing gases which have the characteristic that notwithstanding that ionization occurs, the space between theelec'trodes is nevertheless of greater conductivity in one direction than in the other.

I claim:

1. In an X-ray tube, a cathode and an anode, a radio-active substance associated with the cathode and being of a character that its emissions constitute or carry opposite electrical charges, and means for intercepting one kind of said emissions and permitting the passage of the other kind of said emissions to thereby render the space between the cathode and anode of greater conductivity in. one direction than in the other. 7

2. In an X-ray tube, a cathode and an anode, a radio-active substance associated with the cathode and of a character to emit both alpha and beta rays, and means to' intercept the alpha rays to thereby render the space between the cathode andanode of greater conductivity in one direction than in the other. p I

3. In an X-ray tube, a cathode and an anode, a radio-active substance applied to said cathode and of a character to emit both alpha and beta rays, and a thin metal screen enclosing said radio-active substance and serving to intercept the alpha rays emitted by said radio-active substance and permitting the passage of the beta rays to bomhard the anode and produce X-rays.

4. In 'a gap device forthe passage of electrical current, an electrode having an internal pocket or recess, and a radio-active substance disposed within the pocket and encased in the body of said electrode, whereby the emissions of said radio-activesubstance in order to escape must necessarily pass through a portion of said body.

5. In a gap device for the passage of electrical current an electrode, a radio-active substance associated therewith and of a kind both alpha and beta rays, and a thin metal emitting both alpha and beta rays, and a screen enclosing said radio-active substance screen over said radio-active substance and and serving to suppress the alpha rays. 1 serving to suppress one kind of said rays. In testimony whereof, I- sign my name.

6. In a gap device for the passage of elec- GROVER R. GREENSLADE. trical current, an electrode, a radio-active Witness:. substance associated therewith and emitting EDWIN O. JOHNS. 

